1 files changed, 98 insertions, 0 deletions
diff --git a/plugins/extraction/ExtrOcamlBigIntConv.v b/plugins/extraction/ExtrOcamlBigIntConv.v
new file mode 100644
index 000000000..9f80812db
--- /dev/null
+++ b/plugins/extraction/ExtrOcamlBigIntConv.v
@@ -0,0 +1,98 @@
+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(** Extraction to Ocaml: conversion from/to [big_int] *)
+
+(** The extracted code should be linked with [nums.(cma|cmxa)] *)
+
+Require Import Arith ZArith.
+
+Parameter bigint : Type.
+Parameter bigint_zero : bigint.
+Parameter bigint_succ : bigint -> bigint.
+Parameter bigint_opp : bigint -> bigint.
+Parameter bigint_twice : bigint -> bigint.
+
+Extract Inlined Constant bigint => "Big_int.big_int".
+Extract Inlined Constant bigint_zero => "Big_int.zero_big_int".
+Extract Inlined Constant bigint_succ => "Big_int.succ_big_int".
+Extract Inlined Constant bigint_opp => "Big_int.minus_big_int".
+Extract Inlined Constant bigint_twice => "Big_int.mult_int_big_int 2".
+
+Definition bigint_of_nat : nat -> bigint :=
+ (fix loop acc n :=
+  match n with
+   | O => acc
+   | S n => loop (bigint_succ acc) n
+  end) bigint_zero.
+
+Fixpoint bigint_of_pos p :=
+ match p with
+  | xH => bigint_succ bigint_zero
+  | xO p => bigint_twice (bigint_of_pos p)
+  | xI p => bigint_succ (bigint_twice (bigint_of_pos p))
+ end.
+
+Fixpoint bigint_of_z z :=
+ match z with
+  | Z0 => bigint_zero
+  | Zpos p => bigint_of_pos p
+  | Zneg p => bigint_opp (bigint_of_pos p)
+ end.
+
+Fixpoint bigint_of_n n :=
+ match n with
+  | N0 => bigint_zero
+  | Npos p => bigint_of_pos p
+ end.
+
+(** NB: as for [pred] or [minus], [nat_of_bigint], [n_of_bigint] and
+    [pos_of_bigint] are total and return zero (resp. one) for
+    non-positive inputs. *)
+
+Parameter bigint_natlike_rec : forall A, A -> (A->A) -> bigint -> A.
+Extract Constant bigint_natlike_rec =>
+"fun fO fS ->
+ let rec loop acc i = if Big_int.sign_big_int i <= 0 then acc
+  else loop (fS acc) (Big_int.pred_big_int i)
+ in loop fO".
+
+Definition nat_of_bigint : bigint -> nat := bigint_natlike_rec _ O S.
+
+Parameter bigint_poslike_rec : forall A, A -> (A->A) -> (A->A) -> bigint -> A.
+Extract Constant bigint_poslike_rec =>
+"fun f1 f2x f2x1 ->
+ let rec loop i = if Big_int.le_big_int i Big_int.unit_big_int then f1
+ else
+  let (q,r) = Big_int.quomod_big_int i (Big_int.big_int_of_int 2) in
+  if Big_int.sign_big_int r = 0 then f2x (loop q) else f2x1 (loop q)
+ in loop".
+
+Definition pos_of_bigint : bigint -> positive := bigint_poslike_rec _ xH xO xI.
+
+Parameter bigint_zlike_case : forall A, A -> (bigint->A) -> (bigint->A) -> bigint -> A.
+Extract Constant bigint_zlike_case =>
+"fun f0 fpos fneg i ->
+  let sgn = Big_int.sign_big_int i in
+  if sgn = 0 then f0 else if sgn>0 then fpos i
+  else fneg (Big_int.minus_big_int i)".
+
+Definition z_of_bigint : bigint -> Z :=
+ bigint_zlike_case _ Z0 (fun i => Zpos (pos_of_bigint i))
+                     (fun i => Zneg (pos_of_bigint i)).
+
+Definition n_of_bigint : bigint -> N :=
+ bigint_zlike_case _ N0 (fun i => Npos (pos_of_bigint i)) (fun _ => N0).
+
+(*
+Extraction "/tmp/test.ml"
+  nat_of_bigint bigint_of_nat
+  pos_of_bigint bigint_of_pos
+  z_of_bigint bigint_of_z
+  n_of_bigint bigint_of_n.
+*)
+\ No newline at end of file